Radiation has widespread effects on cell

["Sandy Perle" <sandyfl@earthlink.net>]

Monday April 26 6:47 PM ET 

Radiation has widespread effects on cell

NEW YORK, Apr 26 (Reuters Health) -- Although it is widely held 
that radiation only has cancer-causing effects when it strikes the 
nucleus, or ``command center'' of a cell, a new study suggests that 
radiation can also trigger cancer through its effects on the cell 
cytoplasm, the fluid medium that fills the cell.  

Reporting in the Proceedings of the National Academy of 
Sciences, a team of scientists showed that irradiating the cell's
cytoplasm but avoiding irradiating the nucleus caused the rate of 
mutations to the cell's genetic material (DNA) to rise as much
as threefold above normal.

Radiation damages cells, causing changes or mutations in the 
genetic material. If a mutant cell reproduces abnormally, cancer
risk is greatly increased.

``The nucleus has always been considered the quintessential 
target for any (cancer-causing) mutation,'' explained lead
researcher Dr. Tom K. Hei, an associate professor of radiation 
oncology and public health at Columbia University College of
Physicians and Surgeons in New York. ``We have learned that if 
you hit the cytoplasm... there is a chance that you will (cause
changes in the nucleus).''

The new findings suggest that public health officials may have to 
alter cancer risk estimates for people who are exposed to low
levels of radiation via radon and repeated x-rays.

Radon is an invisible and odorless gas that is found in the earth, 
rock, well-water and building materials. It has been linked to
an increased risk of lung cancer in humans.

To arrive at their findings, Hei and colleagues used a state-of-the-
art microbeam to irradiate the cell cytoplasm with alpha particles, 
the radiation emitted by radon. After irradiating thousands of cells, 
the investigators found that cells hit by eight alpha particles 
showed a mutation rate that was threefold higher than normal.  

Hei explained that these mutations are different from those caused 
by irradiating a cell nucleus which causes damage in large 
sections of the DNA and typically kills the entire cell. When 
radiation strikes the cytoplasm, the damage is smaller. Fewer cells 
are killed, thus there is a greater risk that abnormal cells can divide 
and spur cancer.  

Cytoplasmic irradiation may play a significant role in causing 
cancer, researchers concluded.

``Cytoplasmic irradiation should be considered a major concern to 
human health in terms of risk of exposure for cancer and birth 
defects, as well as having a profound impact on our understanding 
of the relationship between radiation exposure and diseases,'' Hei 
and colleagues conclude.  

SOURCE: Proceedings of the National Academy of Sciences 
1999:96:4959-4964.
--------------

Monday April 26 5:41 PM ET 

Radiation May Cause DNA Changes

WASHINGTON (AP) - Cells may be more sensitive to genetic 
damage caused by radiation from radon gas than previously 
believed, according to research that found high energy particles do 
not need to hit the nucleus of a cell to cause DNA changes.  

In a laboratory study to be published Tuesday, researchers aimed 
alpha particles - a decay product from radon gas - at the fluid 
surrounding nuclei in cells taken from a hamster, and they found 
that radiation could cause genetic changes.  

``The prevailing view has been that in order to cause genetic 
damage you have to irradiate the DNA directly in the cell nucleus,'' 
said Gerhard Randers-Pehrson of Columbia University, a co-author 
of the study in the Proceedings of the National Academy of 
Sciences. ``What we find is that you can irradiate outside of the 
nucleus and still cause that type of damage.''   

Randers-Pehrson said scientists who calculate the health effects of 
radiation exposure will have to take this new finding into account, 
but that it is not yet clear how the research will affect the risk 
estimates.  

``It may turn out there is more damage to the DNA at low doses 
than previously assumed, but that is something that scientists who 
make these extrapolations will have to determine,'' said Randers-
Pehrson. ``It is unclear as yet whether the results imply greater or 
lesser risk.''  

Exposure to radon gas, a natural byproduct from the decay of 
uranium and radium in soil and rocks, is thought to cause about
21,000 American lung cancer deaths annually, second only to 
smoking.

Radon gas can leak from the earth and collect in basements. 
When inhaled, the gas can leave in the lungs alpha particles that
emit low levels of radiation over long periods of time.

Just how much radon poses a health risk has been controversial, 
but the Environmental Protectection Agency recommends that the 
concentration of radon gas in homes be kept below 4 picocuries (a 
measure of radiation) per liter of air. A National Academy of 
Sciences study last year estimated that since 1980, Americans 
have spent about $400 million on radon gas tests and on 
renovations to vent buildings where the gas can collect. The study 
estimated that about 6 percent of American homes have radon 
concentrations that would merit corrective action.  

Radon cancer risk estimates have been based, in part, on the 
belief that mutations that can lead to cancer occur only if radiation
particles directly hit the cell nucleus that contains the DNA.

In the new study, Randers-Pehrson and his colleagues used a 
machine to zap cytoplasm, the part of the cell outside of the
nucleus, with precise numbers of alpha particles. The number of 
particles is representative of the intensity of radiation exposure.

They found that cytoplasm hits of three to eight particles could 
trigger a genetic change in a cell. Randers-Pehrson said they
also found that when the cytoplasm was hit, the cells tended to 
survive and were more likely to pass mutations into new
generations of cells, a critical step in the formation of cancer.

Alpha particles striking the DNA directly tends to cause such 
extensive damage that the cell is generally killed and does not
make new cells, he said.

Andrew J. Grosovsky, a radiation biologist at the University of 
California, Riverside, said the Columbia University study may
``prompt a reassessment'' of the risks of radon gas. But he noted 
that ``it is way too early to tell what the consequences of this
new understanding will be'' in recommendations about radon gas 
exposure. 

Sandy Perle
E-Mail: sandyfl@earthlink.net 
Personal Website: http://www.geocities.com/capecanaveral/1205

"The object of opening the mind, as of opening 
the mouth, is to close it again on something solid"
              - G. K. Chesterton -
************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html